The overall goal of this research is the development and validation of improved methods for computing epicardial potential distributions, isochrones, and electrograms from body surface potentials. These methods will be used to characterize normal and abnormal electrical cardiac behavior noninvasively through an inverse procedure. The utility of the inverse procedure depends ultimately on the degree of accuracy and spatial resolution with which epicardial potentials can be recovered. We propose to apply theoretical studies, computational simulations, and animal experiments to establish the limits of accuracy and spatial resolution of the inverse procedure. A solution to the inverse problem in electrocardiography would provide a noninvasive means for the evaluation of myocardial ischemia, the localization of the site of origin of ventricular arrhythmias and the site of accessory pathways in Wolff-Parkinson-White (WPW) syndrome, and, more generally, the determination of patterns of excitation and of recovery of excitability. Specifically, by comparing potential distributions gathered from experiments with an electrolytic tank that utilizes realistic geometry with those obtained from simulations using a computer model which is the computational equivalent of the electrolytic tank, we will be able to quantitatively measure how the accuracy of electrocardiographic forward and inverse problems depend on the: resolution of the geometric model, inclusion of anisotropic inhomogeneities, and numerical techniques employed. Furthermore, we propose to use computer models based entirely on human data to evaluate the utility of the inverse procedure for specific pathologies.